1. Field of the Invention
This invention relates to a sterically regulated methacrylic polymer and a process for producing the same. The sterically regulated methacrylic polymer of the invention is a homopolymer or copolymer of methacrylates containing units based on methacrylates each having a tertiary amino group bound to at least two aromatic rings, and has a narrow molecular weight distribution and highly syndiotactic or isotactic linkages. The sterically regulated methacrylic polymer of the invention is useful as a hole-mobile polymer and can be used in an electroluminescence material, photorefractive material etc.
2. Description of the Related Art
It is known that a highly sterically regulated polymer can be obtained from methyl methacrylate which is a typical methacrylate type by low-temperature radical polymerization or low-temperature anionic polymerization. It is known that the methacrylic polymer thus obtained has higher stereoregularity and a narrower distribution of molecular weights than those of methacrylic polymers synthesized by usual radical polymerization, is excellent in moldability, and has specific characteristics.
Heretofore, the stereoregular polymerization of methyl methacrylate has been extensively studied. For example, when methyl methacrylate is polymerized by adding ZrMe2 (in this specification, Me refers to CH3) or Zr(C2H5)2 and B(C6F5)3 to ethylene bisindenyl, a highly isotactic polymer is obtained, but its number-average molecular weight is as low as 20,000 and the yield is also as low as 38% (K. Soga, H. Deng, T. Yano, T. Shion, Macromolecules, 27, 7938, 1994). Further, a method of using a Grignard reagent, a method of using lithium as an initiator in liquid ammonia, and a method of using 1,1-diphenylhexyl lithium are known. In these methods, relatively monodisperse (Mw/Mn˜about 1.5) poly(methyl methacrylate) can be obtained, but these methods are insufficient to prepare the polymer having a high molecular weight, a narrower distribution of molecular weights, and high tacticity.
Various studies have been made to solve the problem described above. For example, use of a trivalent lanthanoid complex as a catalyst for polymerization of methyl (meth)acrylate has been disclosed in recent years by Yasuda et al. (JP-A 3-263412). In this method, poly(meth)acrylic ester having a very narrow dispersion degree of 1.04, a high molecular weight (Mn=194000) and 80% or more syndiotacticity in 3-units expression (%rr) can be produced in 98% yield.
Yasuda et al. have also disclosed e.g. M[C(SiR)3]n (M is a rare earth element, R is a hydrogen atom, an alkyl group, an aryl group, a cycloalkyl group or an arylalkyl group, and n is 2 or 3) as a polymerization catalyst giving polymethacrylate having high stereoregularity, a narrow distribution of molecular weights and high isotacticity (JP-A 10-265517).
On one hand, a polymer containing a triphenyl amino group in a side chain is an excellent organic photoconductive (specifically highly hole-mobile) material and is thus noted in recent years as an optoelectronics organic polymer material. For example, as disclosed in JP-A 10-333195, the polymer containing a triphenyl amino group in a side chain has been revealed in recent years to give excellent hole mobility.
The polymer giving such hole mobility is known to be applicable to electrophotographic radiation sensitive materials, electroluminescence materials and photorefractive materials. However, a process for efficiently producing methacrylic polymers having high stereoregularity and a narrower distribution of molecular weights and containing a high-molecular-weight triphenyl amino group in a side chain is not known until now.